1. Field of the Invention
The field of the invention is power conversion, or, more specifically, methods operating a DC-DC converter and coupled inductors for use in a DC-DC converter.
2. Description of Related Art
Computer system technology is continually advancing. Data centers, for example, now include hundreds or thousands of servers. Given the number of servers in a data center, decreasing the physical size or ‘footprint’ of the servers is a top priority for server system and server component designers. One area of focus, for example, is in reducing the size of Direct Current (‘DC’)-DC converters that distribute DC power amongst components of servers and the like.
In current art, reducing the size of such DC-DC converters is limited, at least in part, by the need for a plurality of output inductors and a filter capacitor. Some DC-DC converters of the prior art have implemented designs to somewhat reduce the physical footprint of the inductors and the capacitor by utilizing a single magnetic core for multiple inductors—an implementation of an indirectly coupled inductor. FIG. 1, for example, sets forth a prior art DC-DC converter that includes an indirectly coupled inductor.
The example DC-DC converter (100) of FIG. 1 includes two power-switching phases (132, 134). Each phase includes two switches: a high-side switch (102, 106), and a low-side switch (104, 108). Each high-side switch (102, 106) includes a control input (110, 114) to activate the switch. Upon activation, each high-side switch (102, 106) couples a voltage source (VIN) to an indirectly coupled inductor (118). Each low-side switch (104, 108) also includes a control input (112, 116) to activate the switch. Upon activation, each low-side switch (104, 108) couples one coil of indirectly coupled inductor (118) to a ground voltage.
Coupled inductors come in two forms: indirectly coupled and directly coupled. The dots depicted in the example of FIG. 1 indicate the coupled inductor (118) is an indirectly coupled inductor. The dot convention specifies the flow of current in a coupled inductor as: when current flows ‘into’ one dot, current is induced in the alternate coil of the coupled inductor and flows ‘out of’ the other dot. Thus, in an indirectly coupled inductor, current generally flows in the same direction in both coils of the coupled inductor.
The example prior art DC-DC converter (100) of FIG. 1 also includes an output capacitor (120) that operates as a filter and a load, represented by a resistor (122).
FIG. 2 sets forth an example timing diagram (130) of activating the switches (102, 112, 106, 116) of the prior art DC-DC converter (100) of FIG. 1. In the example timing diagram of FIG. 2, switch (102) is activated between time T0 and T1, then deactivated from T1 through T3. Switch (112) is not activated from time T0 and T1, but is activated at time T1 through T3. Switch (114) is only activated between time T2 to T3. Switch (116) is activated from time T0 to T2 and activated again at time T3.
The timing diagram (130) in the example of FIG. 2 specifies that activation of the high-side switch and low-side switch in a single phase of the prior art DC-DC converter (100) of FIG. 1 is asynchronous. Further, during any one given time period, two of the switches are activated at the same time. Although the indirectly coupled inductor in the example prior art DC-DC converter (100) of FIG. 1 represents a reduction in size relative to two, discrete inductors, operating the indirectly coupled prior art DC-DC converter (100) in accordance with the timing diagram of FIG. 2 limits any further inductor and capacitance reduction due to many factors, including for example: efficiency, current ripple, and so on.